DESCRIPTION: The secretion of neurotransmitter chemicals at synapses is the basis for transmission and storage of information within the brain. Neurotransmitters are secreted in response to a transient rise in the concentration of calcium ions within presynaptic terminals and the general goal of this project is to understand how this rise in presynaptic calcium concentration leads to secretion of neurotransmitters. It is widely hypothesized that proteins found in presynaptic terminals mediate neurotransmitter release. Although great progress recently has been made in identifying proteins that are found on synaptic vesicles, the plasma membrane, or elsewhere within the presynaptic terminal, the roles of these proteins in transmitter release are largely unclear. Thus, the specific goal of this project is to test such molecular hypotheses of transmitter release by identifying the function of several of these presynaptic proteins. Attention will be focused on proteins that interact with function of several of these presynaptic proteins. Attention will be focused on proteins that interact with SNARE complex proteins, such as complexin, unc-13, VAP-33 and AP-3, as well as the sec6/8/15 proteins that are proposed to act before the SNARE complex. Because these proteins are thought to act by binding to other proteins, the functional importance of binding of these proteins to each other also will be assessed. To test the hypothesis that each of these proteins, or protein-protein interactions, is involved in transmitter release, reagents that perturb these proteins or their interactions will be microinjected into living presynaptic terminals. Such reagents will affect release from these terminals only if the hypothesized protein, or interaction, is important for release. By looking at the timing and intracellular mechanism of action of these reagents, they also will begin to define the temporal order in which these proteins act in transmitter release. Because few synapses have presynaptic terminals large enough to permit microinjection, these experiments will be performed on the unique "giant" presynaptic terminal of squid. The investigators experiments will define the molecular mechanisms involved in neuronal communication and, thereby, ultimately clarify the actions of numerous neurological disorders that result from defects in this communication.